Studies are proposed that will elucidate the structural changes occuring in during force transduction in muscle by myosin crossbridges and the structural changes the sarcoplasmic reticulum calcium transport ATPase during ion pumping. Both processes are of fundamental importance to muscle physiology in particular and cell physiology in general. Crossbridge states will be studied by 3-dimensional and 2-dimensional image analysis procedures applied to electron micrographs of sectioned insect flight muscle. Stable muscle states to be examined include rigor, two states produced by AMPPNP, and relaxed muscle. The position of the troponin complex will be determined using monoclonal antibodies to troponin. The studies of myofibril structure will be correlated to determine the structural parameters regulating crossbridge binding in various states, the effects of crossbridge binding upon thin filaments and the structural changes occurring in the crossbridges under the different conditions which may hope to mimic states in the crossbridge cycle. Rigor will be used as a model for the end of the mechanical force generating stroke, AMPPNP for an attached-non rigor state and relaxed muscle for the detached crossbridge state. Fourier-Bessel 3-dimensional image reconstructions of actin filaments decorated with single headed heavy meromyosin and of insect flight muscle thick filaments will be done using specimens preserved for electron microscopy in vitreous ice. These studies complement the in situ work by providing a more detailed picture of two important components of the contractile apparatus. Computer modelling studies are proposed which will correlate the results obtained in the various muscle studies. The molecular changes in the Ca2+ transport ATPase during ion transport will be elucidated by structural studies of crystals of the enzyme produced under different conditions. Crystallization conditions used produce stable states of the enzyme which may relate to the ion transport process. Three dimensional reconstructions will be done using electron micrographs negatively stained specimens to determine the aqueous regions of the structure and on frozen hydrated specimens to determine the protein distribution within the membrane bilayer. Correlation of structural changes in the different crystal forms with kinetic steps in the enzyme pathway will be carried out.